There is enormous interest in the development of stem cells for a wide variety of uses in research, veterinary science and medicine. Amongst the potential uses is their application in cell-based therapies for treating diseased or damaged tissues (ie so-called regenerative medicine). For example, stem cells can be used to produce neural stem cells that may be able to regenerate nerve tissue damaged by spinal injury.
Central to the further development and success of regenerative medicine is the identification of safe and cost-effective sources of suitable stem cells. Thus, considerable research has been directed at developing processes for producing autologous stem cells, such as patient-specific pluripotent stem (PS) cells. One highly significant development from this research has been the finding that fibroblasts (which can be readily and, in some cases, relatively non-invasively obtained from the patient) can be reprogrammed into induced pluripotent stem cells (iPS) and induced epiblast stem cells (IEpiS)1-10, for example, by introducing polynucleotides encoding peptide reprogramming factors, or by directly introducing polypeptide reprogramming factors (eg transcription factors and other factors associated with reprogramming, such as Oct-3/4 (Pou5fl), Sox family (eg Sox1, Sox2, Sox3, Sox15, Sox18, etc), Myc family (eg c-Myc, N-mvc, L-myc), Klf family (eg Klf1, Klf2, Klf4, Kf15, etc), Nanog, Lin28 etc). Such polynucleotide or polypeptide reprogramming factors can be introduced into cells as genetic material using viral transfection vectors (eg retroviruses), or plasmids, or be introduced as mRNA or miRNAs, or as polypeptides (eg recombinant polypeptides). However, in despite of the remarkable progress that has been made in the last five years in iPS cell research, the hope of the clinical utilisation of pluripotent stem cells for the treatment of human diseases has remained elusive, mainly due to the risks (eg potential to induce cancer) associated with viral transfection vectors and/or exogenous and potentially oncogenic transcription factors and related factors associated with reprogramming that are presently used for the induction of the pluripotent stem cells.
Recently, research has elucidated a way by which various small molecules can be used to replace certain polypeptide or polynucleotide reprogramming factors (such that fewer transcription factors can be used in the induction) so as to improve the stem cell induction efficiency and diversity in the reprogramming process11-21,49. Intrigued by such research, the present applicant set out to determine whether it may be possible to produce iPS using only small molecules and, thereby, enable the development of new processes for stem cell induction offering improvements in safety and, possibly, efficiency. Using a selection of one or more small molecules, the present applicant was unable to produce iPS but has been able to induce somatic cells such as fibroblasts into multipotent cells such as neural stem cells without the use of any polynucleotide or polypeptide reprogramming factors such as viral transgenic vectors and/or oncogenic transcription factors. The resultant small molecule-induced neural stem (SMINS) cells closely resemble native neural stem (NS) cells in morphology, gene expression patterns, self-renewal and multipotency.